Electrode structure for a charged particle accelerating apparatus, arrayed and biased to produce an electric field between and parallel to the electrodes



Oct. 22, 1968 E. E. HAND ELECTRODE STRUCTURE FOR A CHARGED PARTICLEACCELERATING APPARATUS. ARRAYED AND BIASED TO PRODUCE AN ELECTRIC FIELDBETWEEN AND PARALLEL TO THE ELECTRODES 4 Sheets-Sheet 1 Filed May 23,1966 FIG. I PRIOR ART FIG. 3

INVENTOR EUGENE E ND BY f r I) W ATTORNEY Oct. 22, 1968 E. E. HAND3,407,323

ELECTRODE STRUCTURE FOR A CHARGED PARTICLE ACCELERATING APPARATUS,ARRAYED AND BIASED To PRODUCE AN ELECTRIC FIELD BETWEEN AND PARALLEL ToTHE ELECTRODES Filed May 23, 1966 4 Sheets-Sheet 2 unnmunF-E..

lNVENTOR EUGENE E.HAND

BY f

ATTORNEY Oct. 22, 1968 E. E. HAND 3,407,323

ELECTRODE STRUCTURE FOR A CHARGED PARTICLE ACCELERATING APPARATUS,AREAYED AND BIASED TO PRODUCE AN ELECTRIC FIELD BETWEEN AND PARALLEL TOTHE ELECTRODES Filed May 23 1966 4 Sheets-Sheet I5 FIG. 6

1+ STRONGER WEAKER FIG. 7

INVENTOR EUGENE E. H ND W ATTORNEY 0d. 22, 1968 E. E. HAND 3,407,323

OR A CHARGED PARTICLE ACCELERATING AND BIASED TO PRODUCE AN ELECTRIC NDPARALLEL TO THE ELECTRODES ELECTRODE STRUCTURE F APPARATUS, ARRAYEDFIELD BETWEEN A 1966 4 Sheets-Sheet 4 Filed May 23 .alllllllllllllh 9Ollllllllllllllllll Vlllllllllllllll v I v INVENTOR EUGENE E. AND

TORNEY United States Patent 3,407,323 ELECTRODE STRUCTURE FOR A CHARGEDPARTICLE ACCELERATING APPARATUS, ARRAYED AND BIASED T0 PRODUCE ANELECTRIC FIELD BETWEEN AND PARAL- LEL TO THE ELECTRODES Eugene E. Hand,Andover, Mass., assignor to High Voltage Engineering Corporation,Burlington, Mass., a corporation of Massachusetts Filed May 23, 1966,Ser. No. 560,360 11 Claims. (Cl. 313-63) ABSTRACT OF THE DISCLOSURE Anapparatus for moving a charged particle beam which consists of a pair ofelectrodes, having a controlled resistance drop in one direction, whichhave been biased to produce equipotential lines between the electrodessuch that the resultant electric field between the electrodes isparallel to the electrodes.

This invention relates generally to the manipulation of charged particlebeams and more particularly to a novel electrode structure formanipulation of charged particle beams by electric fields.

Both magnetic and electrostatic systems have been used to manipulatecharged particle beams. In most applications electrostatic systems arepreferred over magnetic systems for they are linear and do not exhibithysteresis or residual fields. All prior art electrostatic beam handlingsystems basically comprise a pair of opposed electrodes with potentialsapplied between them to produce an electric field normal to theelectrode surface. Such systems are exemplified by the electrostaticdeflection plates found in cathode ray tubes.

Although this system is widely known and used it has an inherentlimitation in that a m nimum width to gap ratio must be maintained toprovide uniform fields between the electrodes. Therefore, to achievemeaningful electrode gaps the opposing electrode areas must berelatively large. With increasing electrode area the probability ofelectric breakdown of the applied electric field, across the single gap,increases proportionately with the electrode area.

Furthermore, with increasing electrode area it becomes more difficult tocondition such systems to hold maximum potentials. An increase in thepower required to maintain the desired potential across the gap occursbecause currents exist across the single gap even when a chargedparticle beam is not passing through the gap. Moreover, when a beam isintroduced into the gap, breakdown occurs more readily due to cumulativeionization because both random charged particles and their generatedsecondaries are subjected to the total gap potential.

These drawbacks are particularly noted and become quite troublesome insystems which are required to manipulate beams whose particle energy isin the mev. range or higher.

The present invention was designed to avoid and to overcome all thedrawbacks and disadvantages encountered in the prior art electrostaticdeflection systems. The present invention thus provides an electrostaticdeflection system in which the field uniformity, in the central region,is not a function of the width to gap ratio thereby reducing thebreakdown probability and lowering the required power. Additionally thepresent invention minimizes the possibility of unwanted particles beingswept out of the system from impacting the electrodes and causing fieldperturbations and eliminating cumulative ionization to reduce theloading of the system.

Moreover, the invention may be used as a beam scoop to extract a portionof a beam from a chamber without disturbing the remainder of the beam.

Broadly speaking, these and other advantages and features of the presentinvention are obtained by biasing a pair of opposing electrodes toproduce equipotential lines between the electrodes such that theresultant electric field between the electrodes is parallel to theelectrodes.

The present invention and various modifications and embodiments thereofwill be best understood by perusal of the following specification takenin conjunction with the attached figures wherein:

FIG. 1 illustrates the field and equipotential lines of the prior art.

FIG. 2 illustrates one embodiment of the invention.

FIG. 3 an end view of the embodiment of FIG. 1 shows the power supplycircuit and field and equipotential lines.

FIG. 4 shows a different embodiment of the invention.

FIG. 5 shows a modified electrode array.

FIG. 6 illustrates the invention used as a storage ring.

FIG. 7 shows the apparatus of FIG. 6 modified by the incorporation of -adumping section.

FIG. 8 illustrates the invention used as an electrostatic orbitalaccelerator.

FIG. 9 shows the apparatus of FIG. 4 used as a beam scoop.

FIG. 10 shows still another embodiment of the electrode array.

FIG. 11 illustrates the invention used as an RF beam separator, and

FIG. 12 illustrates another embodiment of the invention using resistivematerials as the electrodes.

Considering first the prior art there is shown in FIG. 1 the simple caseof a pair of flat parallel metal plates 10 and 11 that are oppositelycharged by a battery 12. Immediately upon the charging of the plates,field lines, shown as solid arrows 13, are produced and extend acrossthe gap 14 from plate 10, positively charged, to plate 11, negativelycharged. Simultaneously, equipotential lines, shown by dashed lines 15,are created parallel to the plates and perpendicular to the field lines.Because the plates are not infinite in length the field andequipotential lines become distorted at the plate edges.

If a beam of charged particles, for example electrons or ions, arepermitted to pass between these plates under the above conditions, thecharged particle means will be deflected along the field lines towardsthe oppositely charged plate. If the applied plate polarity is reversed,the deflection will also be reversed. In such a device particles ofdifferent velocities traverse the field in different times andconsequently are deflected by correspondingly different amounts.

Turning now to FIGS. 2 and 3 the basic principles of the invention willbe described. In these views the invention has been reduced to itssimplest components and is shown as a first elctrode array 21 and asecond electrode array 22 contained within a hollow evacuated chamber 20which contains an opening 26 through which charged atomic or nuclearparticles may pass. Each array comprises a multiplicity of rodelectrodes held in a rigid stacked arrangement by a plurality ofinsulating standolf spacers 32 which serve to isolate the electrodesfrom each other and from the walls of chamber 20 which is at groundpotential 25. In this view the electrodes comprising array 21 arenumbered 27, 28, 29, 30 and 31. While the electrodes comprising array 22are numbered 27a, 28a, 30a and 31a. Although five electrodes are shownin each array it should be understood that this number can be increasedor decreased or greatly modified, as will be discussed later, and stillremain within the scope of the present invention.

Each electrode is electrically connected through resistors to a suitablepower supply shown as batteries 23 and 24 to impose a voltage gradientbetween each electrode in the array. The central electrode in each arrayis grounded and is coupled to each adjacent electrode by a droppingresistor which in turn is coupled to its adjacent electrode by aresistor, with the outer most electrodes being connected directlly tothe power supplies.

Thus, for example, in array 21 electrode 29 is grounded'and connected toelectrodes 28 and 30 by means of dropping resistor 33 and 34respectively. Electrode 28 is, in turn, coupled to its adjacentelectrode 27 through a resistor 35. Electrode 27 being the end electrodeis coupled directly to the positive side of supply 23 whose negativeside is tied to ground 25. Electrode 30 is coupled via resistor 36 toelectrode 31 which is directly connected to the negative side of supply24 whose positive side is tied to ground 25. Array 22 is coupled in asimilar manner to the same power supplies as shown in FIG. 2.

This creates electrical pairing of the two arrays and creation ofelectric field lines 36 between and parallel to the arrays. Thus thefield lines 36 are lateral to or parallel to the arrays. Since eachelectrode in an array is electrically paired with its counter-part inthe other array, that is electrode 27 is paired with electrode 27a, 28with 28a, 29 with 29a, 30 with 30a and 31 with 31a, equipotential lines27b through 31b are established between each electrode pair.

A stream of charged particles passing between the arrays becomesdeflected along the field lines. However, in this case the field linesare parallel to the array of electrodes and not perpendicular thereto.

With this electrode construction, the field uniformity in the centralregion becomes a function of the distance of the central region from thelocal field distortion near the individual electrodes. The total appliedpotential is divided uniformly across the gaps between the electrodes,thus reducing the effect of electrode area. Because the total appliedvoltage is broken into discrete steps the probability of breakdownbetween the electrodes is small. This will perhaps be better understoodfrom the following brief discussion regarding ionization in the system.

In the first case we will assume that, as shown in FIG. 3, a positivelycharged ion 37 exists either at the surface of electrode 27 or in thegap between the electrodes 27 and 28. The applied electrostatic forceswill urge this ion along the field lines toward the negatively chargedelectrode 30. However, it will be diflicult if not impossible for thision, because of the field geometry, to travel to any other electrodeexcept electrode 28. In traversing the gap between electrodes 27 and 28the total energy gained by the ion would be ZeV/n where e is theelectronic charge of the ion, V is the voltage applied and n is thenumber of gaps in the system. The probability of this ion traversing theentire potential 2eV, that is, traveling directly from electrode 27 toelectrode 31 is negligible since the field lines between the electrodesassume the shortest possible length and thus will terminate in the nextadjacent electrode. Additionally the cumulative effects of ionizationare also less since any secondary ions, that are created, wouldexperience the same difiiculty in gaining the total energy 2eV. In theprior art System an ion 38 on the surface of one electrode would uponstriking the opposite electrode have a total energy of 2eV whereupon aloading of the electrode and secondary emission would occur.

In the other case we will assume that an ion 39 exists in the centralregion away from the electrodes on one of the equipotential lines.Considering only the worst case, which is where a positive ion 39 is onthe equipotential line 27b we find the ion can travel to the nearestwall 40 of chamber 20 arriving with an energy 2V, or itcan traverse thefield striking the electrode 31, with an energy 2eV or continue andstrike the opposite wall 41 of chamber 10 with an energy eV.

' Because the area of electrode 31 is small and the proba- 4 bility ofan' ion striking it is also small and the most likely case is that theseions will strike the chamber wall 41 within energy eV. The energy ofparticle 39 when traveling along the field lines toward wall 41 willincrease as it crosses each equipotential line until it reaches amaximum energy 2eV upon crossing line 31b. After crossing line 31b it isdecelerated to an energy eV with 'whichit strikes wall 41. Thusthe'possibility of generating secondary emission from the wall is lessthan that of the prior art.

. The other possibility of generating secondary electrons occurs it theion strikes a gas molecule. Since chamber 20 will, in usage, be highlyevacuated this probability is also small.

The above described probabilities and possibilities also holds true ofsecondary particles. Since, all the ionization currents are reduced thepower required by this system is reduced proportionally.

In the case where a beam is injected between the electrode array alongthe centerline 43 conditions are also improved. I

' When an injected beam having a wide energy spectrum, is introducedinto the chamber along centerline 43,'the diverted particles of unwantedenergy travel along the field direction to strike the chamber walls andnot the electrodes thus eliminating heating of and cumulative ionizationon the electrodes. Furthermore because the injected beam is in thecenter of the system, which is substantially at ground potential, anyions created by the beam striking gas molecules strike the chamber wallsat low energy thus reducing the probability of secondary emission. Theelimination of cumulative ionization on the electrode reducesthe'loading on the system. Furthermore because the chamber walls now actas the collector for unwanted ions the cooling problem is significantlyreduced and the need of elaborate, insulated, electrode cooling systemsis eliminated. All that is now required is that'cooling beapplied'directly to the chamber walls which are at ground potential.

Numerous modifications or embodiments, of the present invention, may nowbecome obvious. For example, by constructing all portions of the devicefrom non magnetic material and placing magnet poles 110 and 111 acrossthe electrode array 21 crossed magnetic field effect may be added to theelectric field whereby increased defiection power is obtained.

Thepresent invention may also be used to deflect charged particle beamsin a circular or semi circular path. FIG. 4 shows an apparatus,utilizing the present invention, designed to turn the beam 90. In thisview a pair of electrode arrays 41 and 42, each consisting of aplurality of equispaced electrodes 51, 51a, 52, 52a, 53, 53a, 54, 54a,55, 55a, 56 and 56a are formed to describe the quadrant of a circle.These arrays are biased in a similar manner as shown in FIG. 3. Thisbiasing arrangement creates an electric field which is directed towardsthe center of circle as shown by field lines 43. This field arrangementcauses a beam entering one end of the structure along a line 45 to bedeflected such that it emerges from the structure along a line 46 whichis at right angles to line 45. When the particles comprising the beamhave different energies they are all deflected diflerent amounts. Inthis case the main portion of the beam will pass out of the structurealong line 46, but those portions, which are of greater energy will passout of the structure along tangents 47 and 48 and those of lesser energywill trave in tighter circular paths 49 or 50.

By providing openings in the chamber wall different mass particles canbe extracted from the chamber without causing perturbations in thecreated electric field.

If it is desired that the entire beam entering along line 45 be emittedalong line 46, even though all particles are not exactly at the sameenergy, the electrode structure may be modified such that this rejectionof different particles is minimized.

This modified electrode structure is shown in FIG. 5, where for the sakeof simplicity and clearness the numerical designations used in FIG. 4will be used again. In this modified structure the electrodes becomemore closely packed as their radius increases. Thus for example,electrodes 51 and 52 are closer together than are electrodes 55 and 56.Additionally, the bias applied to each electrode is varied. For example,electrode 56 could be at ground potential, electrode 55 at somepotential V, electrode 54 at a potential 2V and AV, electrode 53 at apotential 3V+2AV, electrode 52 at a potential 4A+3AV and electrode 51 ata potential 5V+4AV. This electrode and biasing arrangement creates anelectric field which increases in strength proportional to the increasein potential and electrode packing density.

Thus, in this structure, a beam passed into it along the line 45' willbe emitted along the line 46. The entire beam is confined between theelectrodes and will pass out of the array along the line 46 becauseparticles with higher energies etc. will tend to go towards the outsideof the array e.g. towards electrodes 51, 51a where they encounter astronger field which deflects them more strongly while particles withlower energies go towards the inner electrodes 56, 56a where the weakerfield deflects them less strongly.

By taking advantage of this flexibility and by forming the electrodessuch that they assume a ring shape the invention may be utilized as aparticle or beam storage ring. This is shown in FIG. 6. For the sake ofsimplicity only electrodes 56, 56a and 51, 51a are shown. The packingand biasing arrangement can be the same as shown in FIG. 5. In thisdevice the particles introduced into the space between the electrodearrays would remain therein on particular radial paths until released.If the particles are non-relativistic in energy then the required fieldstrength and thence the potentials required on each electrode may bereadily determined from the equation where E is the field, e theelectronic charge, In the particle mass, v the particle velocity and Rthe radius of the desired orbit.

Radial focusing is accomplished by arranging increasing electric fieldoutside the desired radius and decreasing field inside the desiredradius. In this way the particles 4 will be confined to a particularorbit for when they begin to stray they will be returned by the fieldconfiguration. To remove the particle from the ring the field must beextinguished and the particles Will leave on a path tangential to radialpath they were following at that time.

The above described storage ring can be modified such that it will ejectthe stored particles along a particular path or at a desired time. Thisis accomplished by providing in the ring a beam dumping section such asis shown in FIG. 7.

In this device a segment of each ring is isolated from the remainder ofthe ring. These segments are shown as 51c, 56c, 51d which are seperatedfrom their respective rings 51, 56, 51a and 56a by insulating gaps 71and 72. This sectionalized portion 70 is separately biased in the samemanner as the rest of the device. When it is desired to eject thecontained particles, the potentials on this section 70' are decreasedrapidly such as by shorting to ground and the particle beam will emergefrom the storage ring tangentially to the shorted out section.

This invention may also be used as an electrostatic orbital accelerator.This embodiment is shown in FIG. 8. In this view the apparatus is shownschematically, and comprises four semicircular electrode arrays '80, 81,82 and 83 separated by gaps 85 and 86. Each array consists of aplurality of electrodes either as discussed in FIG. 5 or FIG. 1. In thepreferred embodiment the electrode arrangement of FIGS. 2 and 3 would beused. That is, each electrode would be equally spaced from each otherelectrode. For purposes of illustration only three electrodes are shownin each array, a positive, a negative and a ground. Each electrode wouldbe separately biased such that a radial field is established between thearrays. This radial field will keep an injected particle in apredetermined orbital path. The biasing shown in FIG. 8 is forpositively charged particles. That is the outermost electrodes in eacharray is positive and the innermost electrode at a negative potentialwith the ground electrode centrally located in the array.

Once the particle is injected in the field it follows a semicircularpath of radius proportional to its velocity and orbits around the ringfrom segment to segment. (Thus the invention is a modified cyclotron inwhich an electrostatic field is substituted for the magnetic field.) Bysuperimposing an alternating electric field on the D.C. bias applied tothe electrodes and across the gaps and 86 and this oscillation adjustedsuch that the particle enters the gaps 85 and 8 6 to be pulled by theAC. field, in the direction that it is already traveling and increaseits speed at each crossing of the gaps.

The invention :may also be used as a beam scoop as shown in FIG. 9. Inthis embodiment the electrode arrays are curved as illustrated in FIG.4- and have the same potentials applied thereto. By positioning thisstructure such that it intercepts only a portion of a broad beam thatportion so intercepted may be extracted while leaving undisturbed theremainder of the beam. Such partial extraction is used for measurementpurposes. This configuration may also be used to extract lower energyparticles from a highly energetic beam.

Turning now to FIG. 10 there is shown in schematic cross section anembodiment of the present invention designed to produce high, intensefields while providing long surface insulation paths. In this view, theouter electrodes 180, 181, 183, 184 and 180a, 181a, 183a, 184a are eachformed in a dog-leg manner such that in the central portion of the arraythey become closely packed towards the grounded control electrode 182while at the outer ends they are widely separated and insulated from oneanother by long bar like insulators 85. Such an embodiment is to bepreferred in many applications since the long surface insulation pathsare obtained. If desired the surfaces of the insulators 85 could becorrugated to provide even longer paths.

FIG. 11 shows the invention used as a radio frequency beam velocityseparator. Such separators depend on the mass-dependent velocitydifference among particles in a beam of well defined momentum. In thisapplication four arrays 90, 91, 92 and 93 are used with array 90 beingpaired with array 91 and array 92 paired with array 93. Each array wouldhave potentials applied thereto as illustrated and described in FIGS. 2or 3. Additionally an R-F signal would be superimposed on each arraypair from a suitable generator 94 and 95.

Each R-F separator will be contained in a single chamber 96 butseparated from each other by a suitable drift space. Thus transmit timeof the particles through the pair of arrays and drift space determinesthe relative phase of the particle deflection. With this system theresultant deflection of one particle can be made greater than thedeflection of a different particle while leaving a third particleundisturbed. The amplitude and phase of the deflecting R-F fields mustbe held constant with respect to one another.

Still further this present invention may be modified by changing theshape of the ends of each electrode array so as to cause the fringingelectric fields to be more uniform. Additionally if it is desired todefine the entrance and exit fields accurately for optical reasons, gridwires may be connected between the electrodes which have the highestpotential applied thereto.

Having now described several embodiments and applications of the presentinvention and because other adaptations may now become apparent to thoseskilled in the art, for example the electrode array of individualelectrodes could be replaced by known resistive materials such assemiconductors to provide selected voltage drops without requiringcoupling resistors, such an adaptation is shown in FIGURE 12 whereparallel plates 101 and 102 of controlled resistive material such assheets of semiconductive material are used as the electrodes. Forclarity the surrounding chamber has been omitted from this figure.

To achieve the effects of the present invention these plates 101 and 102must be biased as shown in FIGURE 12, that is to say, one end of a platemust be biased positive, for example, end 103 of plate 101, and its opposite end 105 biased negatively. The other plate 102" must becorrespondingly biased so that end 104 is biased positively and end 106biased negatively. This arrangement creates an electric field in adirection, shown by the arrow 107, which'is parallel to and between theelectrodes 101 and 102. Such electrodes can be used in lieu of thearrays of, for example, FIGURES 2 or 6. Thus it is desired that thepresent invention be limited only by the following claims.

What is claimed is:

1. A charged particle beam manipulation apparatus comprising anevacuated chamber, said chamber being at ground potential only a singlepair of electrode means insulatively maintained in said chamber in planeparallel opposition, means for directing a charged particle beam throughsaid chamber and between said electrode means, each of said electrodemeans having a cont-rolled resistance drop in at least one direction,and power supply means for applying an electric potential to each ofsaid electrode means to establish a controlled voltage drop across eachof said electrode means in the direction of said controlled resistanceto establish an electric field between said electrode means and parallelto the plane of said electrode means, said electric field being in thedirection of said controlled voltage drop, said electrode meanscomprising an array of conductive rods, each rod being resistivelycoupled to the next adjacent rod and insulated from said chamber walls.

2. The apparatus of claim 1 wherein each of said rods are arcuate toform an electrode which describes the quadrant of a circle.

3. The apparatus of claim 1 wherein the conductive rods comprising saidarrays are equally spaced from one another.

4. The apparatus of claim 1 wherein said rods are more densely packed inone direction across said array and said applied potential increases invalue in proportion to said increase in rod density.

5. The apparatus of claim 1 wherein said rods are more densely packed inone direction across said array.

6. A charged particle beam manipulation apparatus comprising anevacuated chamber, said chamber being at ground potential, only a singlepair of electrode means insulatively maintained in said chamber in planeparallel opposition, means for directing a charged particle beam throughsaid chamber and between said electrode means, each of said electrodemeans having a controlled resistance drop in at least one direction, andpower supply means for applying an electric potential to each of saidelectrode means to establish a controlled voltage drop across each ofsaid electrode means in the direction of said controlled resistance toestablish an electric field between said electrode means and parallel tothe plane of said electrode means, said electric field being in thedirection of said controlled voltage drop, each of said electrode meansbeing composed of an array of concentric rings, the innermost of saidrings having the lowest potential applied thereto and the outermost ringhaving the highest potential applied thereto, said applied potentialscreating a radially inwardly directed electric field parallel to theplane of said arrays.

7. The apparatus of claim 1 wherein said electrode means and saidchamber define an arc and a multiplicity of beam exit ports in saidchamber. v

8. A charged particle beam manipulation apparatus comprising anelectrically grounded, evacuated chamber, only a single pair ofelectrode means enclosed in said chamber, said electrode meansinsulatively maintained in said chamber in plane parallel opposition,means for directing a charged particle beam through said chamber andbetween said electrode means and means for creating a charged particledeflection force between said electrode means and parallel thereto, eachof said electrode means being composed of a plurality of concentricrings, said creating means comprising D.C. power supplies coupled tosaid electrode means to create a radial inwardly directed'electric fieldbetween and parallel to the electrode means, and each of said electrodemeans being provided with a segment electrically separable from theremainder thereof, said segments being provided with means for reducingthe field between said segments to zero.

9. A charged particle beam manipulation apparatus comprising anelectrically grounded, evacuated chamber, only a single pair ofelectrode means enclosed in said chamber, said electrode meansinsulatively maintained in said chamber in plane parallel opposition,means for directing acharged particle beam through said chamber andbetween said electrode means and means for creating a charged particledeflection force between said electrode means and parallel thereto, eachof said electrode means comprising a flat circular ring having acontrolled resistivity in a radial direction.

'10. A charged particle beam manipulation apparatus comprising anelectrically grounded, evacuated chamber, only a single pair ofelectrode means enclosed in said chamber in plane parallel opposition,means for directing a charged particle beam through said chamber andbetween said electrode means and means for creating a charged particledeflection force between said electrode means and parallel thereto, eachof said electrode means having a first segment and a second segment,electrical isolation means separating each segment from the othersegment, said creating means comprise DC. power supplies coupled to saidelectrode means to create a radial electric field in the plane of saidelectrodes and an AC. signal source coupled across said electricalisolation means to accelerate charged particles traveling in a circularpath between said electrode means and traversing said isolation means.

11. A charged particle accelerator comprising an evacuated hollowchamber enclosing therein a closed orbital path along which chargedparticles may travel, means for injecting charged particles into saidchamber, means in said chamber for producing radial electric fields toconfine the injected particles to orbital paths, said field producingmeans comprising two arrays of arcuate electrodes electrically insulatedfrom each other and from the chamber, means for applying a DC potentialto each of said arrays to create a radially, inwardly directed, electricfield, and means for applying to each electrode array a high frequencysignal, said signal being synchronized to the velocity of said particleto apply an accelerating electric field to the particle as it travelsfrom one array electrode to the other.

References Cited UNITED STATES PATENTS 2,617,076 11/1952 Schlesinger 3132,574,975 11/1951 Kallmann 313-80 X 2,667,582 l/l954 Backus 2504l.9

JAMES W. LAWRENCE, Primary Examiner.

V. LA FRANCHI, Assistant Examiner.

